This application is a 371 of PCT/JP01/08501 filed on Sep. 28, 2001.
The present invention relates to a radio receiving apparatus for demodulating by using a plurality of received signals obtained with a plurality of antennas, and a method for detecting a delay differential between branches in the apparatus.
A method, in which delay profiles are formed for respective received signals obtained through each antenna in a radio receiving apparatus using a plurality of antennas and are combined is known to be effective for searching paths (see Radio Communication Systems (RCS), the Institute of Electronics, Information, and Communication Engineers (IEICE), Report 99-67, July, 1999).
However, there are cases where delay periods from antennas to receiving baseband processing means vary depending on received signals of each antenna (hereinafter called branch received signals). One of the main reasons for this is the variety in the delay characteristics of receiving filters. Cases like above might render the delay profile combination less effective and might even lead to deterioration. Similarly, in a radio receiving apparatus comprising an array antenna, an apparatus for forming delay profiles using signals combining each branch received signal has a similar problem.
Conventionally, one method for detecting delay differentials between individual branch received signals is to measure on a per path basis the processing times of the filters arranged directly behind antennas and delay periods caused by the resistance on the signal lines between antennas and the baseband processing means and thus obtain the delay differentials.
A second method is to measure on a per path basis the delay period from the point a reference signal is input from an antenna to a radio receiving apparatus to the point this signal reaches a baseband processing means, input a reference signal from the antenna to the radio receiving apparatus, and thus obtain differential delays.
However, in a conventional apparatus, a problem with the first method is that the method requires a number of steps to measure and adjust the processing times of the filters and delay periods on signal lines on each path between an antenna and baseband processing means.
With respect to the second method, there is a possibility that a reference signal becomes an interference source, as the reference signal, which is not required for ordinary transmission and receiving, is input, and it is required that delay periods on respective paths between the antenna and baseband processing means are measured, and adjusted. Another problem is that an ordinary received signal may not be received there between.
The object of the present invention is to detect delay differentials of respective branch received signals between a plurality of antennas and baseband processing means in an easy and accurate manner.
The object is achieved as follows: delay profiles of respective branch received signals received through a plurality of antennas are formed; peaks in each of formed delay profile signals are detected; the maximum peaks are obtained from among the detected peaks in the respective delay profile signals; and average delay differentials between the delay profiles are obtained by averaging out a desired number of delay differentials among the maximum peaks.